The present invention generally relates to a system for retaining a stud or fastener in plastic material which prevents shrink voids or depressions in an opposing side of the material. More specifically, the present invention relates to fasteners, fastener systems, and an article incorporating a fastener which employing ultrasonic insertion techniques to insert the fastener into a piece of material without creating cosmetic defects in the material.
Many fastener systems, fasteners, and methods of inserting fasteners into material have been devised. More particularly, ultrasonic energy generating and directing devices are used to insert fasteners into material by deforming the material of the workpiece around an insertion end of the fastener under the influence of ultrasonic energy. Retention of a fastener in a first workpiece is achieved by providing threads on the fastener such that the material of the workpiece is deformed into thread roots on the fastener. The result of such an ultrasonically inserted fastener is similar to a threaded fastener which is driven into the material except that the ultrasonic insertion operation does not require molding, forming, or drilling a threaded bore for receiving the threaded portion of the fastener.
It should be clear to one skilled in the art that fasteners or studs can be inserted into a first workpiece by tapping a threaded bore in the workpiece for receiving the fastener. When tapping a bore in a workpiece to receive a threaded fastener, a portion of material must be provided in which to tap the bore. This requirement can become problematic when the workpiece is an item such as a vehicle grill or the like having a thin walled structure. A vehicle grill has flat or curved thin walled surfaces which do not provide sufficient material in which to form a threaded bore. Therefore, in order to provide sufficient material to engage a fastener with such a workpiece, a boss or protruding portion of material extending from the grill must be provided. In this regard, the protrusion extends from an attachment side of the grill and extends into the engine compartment of the vehicle. Similarly, if the first workpiece is other than a vehicle grill, the protrusion is formed on a side of the first workpiece which is not visible when the first workpiece is attached to a second workpiece.
With further reference to the vehicle grill example, the grill has a cosmetic side and an attachment side. The manufacturing requirements of the cosmetic side demand that the surface be free of cosmetic defects which would affect the appearance of the assembled vehicle. This problem is exacerbated since plastic is often used to form such grills, and the plastic material is coated with a chrome cosmetic finish. The chrome finish tends to magnify or accentuate any defects such as scratches, depressions, or bumps.
The production of grills using plastic material and a chrome finish has encountered problems in that a protrusion of sufficient size to securely retain a fastener to attach the grill to the vehicle tends to form cosmetic defects on the cosmetic side of the grill. The cosmetic defects are a result of the forming process used to form the protrusion. Forming a protrusion for attaching a fastener to the attachment side of the grill requires that a pin be provided in the mold to produce the bore in the protrusion. When the mold is separated, and the material has not completely cured, removal of the pin from the protrusion bore tends to pull the cosmetic side inwardly forming a concave depression on the cosmetic side of the grill in the proximity of the protrusion. The concave depression on the cosmetic side is considered a defect and is magnified upon applying the chrome finish to the grill. Additionally, disparities between the wall thickness of the protrusion and the wall thickness of the grill results in sinking as the plastic material hardens. The material shrinkage tends to form shrink voids in the cosmetic side of the grill further exacerbating defects on the cosmetic side of the grill.
One way to overcome the problem of cosmetic defects formed on a grill as a result of the forming process is to provide a bridge structure supporting the protrusion a distance away from the attachment side of the grill. The bridge can be formed using webs of material upon which the protrusion is attached. The resulting structure positions the protrusion away from the grill structure, thereby eliminating the sinking or depression problem on the cosmetic side of the grill structure. The webs used to form the bridge are sufficiently thin to prevent formation of shrink voids on the cosmetic side of the grill.
This solution to the sinking and defect problem is quite costly and inefficient because special molds must be provided with shuttles or sliders to support the bridges and protrusions away from the grill structure. If for some reason the location of the protrusions must be changed, the molds must be reconfigured with new shuttle positions. Additionally, depending on the design of the grill structure, use of shuttles in the mold may be impractical because the shuttles require a clearance distance to operate. Further still, the construction and maintenance of molds having shuttles can be quite time consuming and expensive.
As such, it remains a problem to provide a system for attaching a fastener to a workpiece, such as a vehicle grill, which does not result in defects on a cosmetic side of the grill. Prior to the present invention, no acceptable solution to these problems has been known.